Energy management strategy for hydraulic hybrid system with compound accumulator based on dynamic programming

The compound accumulator is an energy storage device composed of one large accumulator and one small accumulator. Compared with traditional single-accumulator hydraulic hybrid vehicles, hydraulic hybrid vehicles based on compound accumulator can switch the working timing of large and small accumulators according to the characteristics of different working conditions, more braking energy can be recovered on the premise of providing enough braking strength. This article is aimed at hydraulic hybrid vehicles based on compound accumulator. First, the key components of the hydraulic system were matched, then according to the engine fuel consumption curve, the engine’s high-efficiency work area is divided, and formulated a rule-based energy management strategy based on the principle of adjusting the engine to work in a high-efficiency area. The internal pressure of the compound accumulator is selected as the state variable, the ratio of the torque of the hydraulic pump/motor to the required torque of the vehicle is the control variable, and the optimal fuel economy of the entire cycle is the objective function, and the mathematical model is established using the dynamic programming algorithm, and compiled a program in MATLAB to obtain the optimal torque distribution relationship between the engine and the hydraulic pump/motor and the optimal working timing of the large and small accumulators. Simulation results show that compared with the traditional hydraulic hybrid vehicle with single accumulator based on initial rules and the hydraulic hybrid vehicle with compound accumulator based on initial rules, the hybrid vehicle with compound accumulator based on improved rules can save fuel by 11.84 % and 5.96 % respectively. The fuel saving potential of the compound accumulator structure and the effectiveness of the improved rule control strategy based on dynamic programming algorithm are verified.